Conventionally, Aluminum (Al) is broadly used as a wiring film of a flat panel display such as a liquid crystal display or an organic EL display and as a wiring film of a touch panel or the like. Recently, miniaturization (narrowing of width) and thinning of a wiring film has been developed, and a wiring film having a lower specific resistance than a conventional one is in demand.
According to the above miniaturization and thinning of a wiring film, a wiring film using copper or copper alloy, which is a material having a lower specific resistance than Al, has been provided.
However, there has been a problem such that the Cu wiring film formed by copper or copper alloy and having a low specific resistance is easily discolored in an atmosphere having humidity. In a case of using a copper alloy containing a large amount of additive elements in order to improve the weather resistance, it leads to an increase of the specific resistance.
Thus, for example, in Patent Document 1, a laminated film in which a protective film formed by Ni—Cu—(Cr, Ti) alloy is formed on the Cu wiring film, and a sputtering target used to form the protective film have been proposed. Since this protective film has a higher weather resistance than that of copper, the protective film can suppress the discoloration of the surface of the Cu wiring film even if the laminated film is stored in the atmosphere.